The search for oil and gas and other minerals has through the years been carried out in shallow inland and offshore waters. Significant deposits of oil and gas are located in those areas. This is particularly true of the immediate offshore and inland waters of the United States Gulf Coast surrounding South Louisiana and East Texas. Marine access to well locations in waters as little as 3 feet in depth is often necessary.
It has been standard practice in the industry to drill and service wells located in these shallow water areas by mounting drilling and workover rigs on barges. Specialized barges have been developed for these purposes. In shallow inland protected waters a submergible barge known as a bay barge is utilized. In deeper waters a similar submergible barge equipped with a deck elevated on columns called a posted barge is often used. The typical barge hull is substantially flat on the bottom and is rectangular in cross-section and has a length varying from 150 to 220 feet, a width varying from 40 to 60 feet and a hull depth of 12 to 14 feet.
The drilling rig and drilling equipment is located on the barge deck. The barge deck also supports an elevated structure for the drilling mast. The hull of the drilling barge is typically notched or keyed out at one end. The drilling rig and mast are located over the keyed area of the barge hull which straddles the desired well location.
Because most of the equipment weight is located in the area of the keyed hull, the barge trim is uneven in that it draws more water on the keyed end than on the end without the key.
The existing drilling barges typically draw from 5 to 8 feet of water when loaded. These rigs are floated and towed to the drilling location. They are then submerged by flooding the barge hull with water until it rests on the water bottom. The flat hull bottom serves as the foundation, supporting the vessel and distributing the barge loads to the supporting water bottom. The water depths in which these drilling vessels can be effectively used varies. Bay barges are more effectively utilized in depths from 5 to 13 feet where the deck can be above the waterline when the barge hull is submerged. Posted barges with elevated decks are used in deeper waters up to 20 feet or more in depth.
It is current practice to utilize these barges in very shallow water locations. These shallow water locations are in areas where the water depth is less than that drawn by the barge. To move the barge the water bottoms are dredged to a depth sufficient to accommodate the barge.
The dredging is time consuming and increases the cost of barge location. The dredging may cause significant harm to the delicate coastal environment. Recent environmental concerns have made dredging permits more difficult to obtain. This has restricted access to areas formally accessible by the conventional barges described above.
In areas where the water depths are adequate to float a barge onto location dredging may still present a functional as well as an environmental concern. The barges once on location are submerged so that the barge rests on the water bottom supporting the drill deck and drilling equipment above the water level. The bearing capacity of the soil on the water bottom must be sufficient to maintain the barge at a fixed lateral and vertical position while the barge and rig is being subjected to wind, wave and tidal action during the drilling operation. This often requires the exiting bottom to be dredged out to a depth sufficient to expose soil of adequate bearing capacity. Shell or other fill material is then used to replace the dredged out area and the barge is pulled over the dredged out area and submerged into the proper location. Then, the barge is often held in place with piling known as spuds.
Replacing the dredged soil with shell is an addition to the cost of the drilling rig location. The shell or soft bottom is often washed away by the wave and tidal action. This can result in the barge and rig being moved off the well location. The barge must be relocated, further increasing the expense of the drilling operation. When using a posted barge in exposed deeper waters subjected to wind and sea conditions of the Gulf of Mexico the barge is unstable and tends to move laterally off of its intended location. Typically, clusters of wood pilings are driven along the outer perimeter of the barge to which the barge is connected to provide stability. Three to five clusters of piling per side may be used. Typically, the wind and wave action often will break or dislodge these piling clusters. This results in the rig moving off location. Posted barges seldom make use of retractable steel piling known as spuds to improve barge stability. When the spuds are mounted externally on the outsides of the barge hull, the width of the barge unit would be increased causing the barge to be too wide to pass through narrow canals and locks. Equipping barges with internally located spuds has been shied away from because the steel spuds commonly bend under load while in use and a spud extended below the barge that is bent or deformed could not be pulled up through the spudwells or ports and the barge could be moved only after great difficulty.
A large number of the posted and bay barges described above have been built. The environmental and functional concerns described renders these existing barges obsolete and unusable in certain coastal areas. Thus, there exists a need to provide a relatively inexpensive way to modify these existing barges so as to effectively eliminate the dredging requirements and improve the stability and bearing area disadvantages now associated with these barges.